The conventional device for AC/AC power conversion realizes control scheme through the implement of the conventional transformer or utilizes AC-DC-AC inverted-type control scheme, thus hardly achieving the purpose of precise control, simple circuit design, and size reduction of the device.
For instance, FIG. 1 illustrates the structure of a transformer that transfers voltage by inductive coupling between its winding circuits. A primary winding of the transformer is connected to an AC power source and thus AC is transformed and transmitted from a secondary winding of the transformer. FIG. 2 illustrates the schematic diagram showing the concept of transmitting an AC voltage signal by utilizing the transformer, and voltage V1 and V2 represent an input AC voltage and an output AC voltage, respectively.
FIG. 3 illustrates waveform transformation of conventional AC/AC conversion. An input sinusoidal wave of the AC signal from an AC power source is converted to a direct current (DC) waveform and the DC waveform is inversed to an output sinusoidal wave of the AC signal. The above process is able to be manipulated by a programmable controller to realize the conventional waveform transformation, but the characteristics the input sinusoidal wave of the AC signal is usually different from the output sinusoidal wave of the AC signal. Therefore, the conventional apparatus for AC/AC conversion is hard to make the characteristics the output sinusoidal wave of the AC signal substantially identical to the input sinusoidal wave of the AC signal, thus causing low power factor and electric network pollution.